/31 netmask

[Antero_Vasconce]

hi 

i am trying to configure a /31 address in VSP 7400 rel 8.6 but always gives error.

“brouter port 1/54 vlan XXXX subnet XXX.YYY.ZZZ.153 255.255.255.254”

 “port 1/54, Invalid IP address”

is this possible or not on VSP?

thanks in adv

Antero

[Tomasz]

Hi,

Some vendors and even Extreme platforms (EXOS or SLX AFAIR, but not VOSS) support /31 where for L3 point-to-point there’s no actual need for network/bcast IP, but IMHO it only makes sense when dealing with a constrained pool of public IPs. Other than that, and minding that /31 is not a standard, it should be possible to discuss and get things straight with the peer service provider.

Cheers,

Tomasz

[bfaltys]

A /31 really has no use as the first IP would be the network address and the 2nd would be the broadcast address. That leaves 0 addresses for you to assign to your brouter port. At a minimum you will need a /30 as recommended. That leaves 2 IPs for hosts/brouters etc.

[Ludovico_Steven]

You might be able to swing it this way..

If the WAN IP address ends in 01 or 10 binary, then simply create the VSP IP ending with 10 or 01 binary (the other way round) but using a /30 mask.

If the WAN IP address ends in 00 or 11 binary, then it’s more fiddly..!

[EXTR_Paul]

that is a very bad news.

FYI…..

31 bit network masks as specified by RFC3021 is not an internet standard.   https://datatracker.ietf.org/doc/html/rfc3021   It is only a “proposed standard”.